A wide range of technologies related to the design and manufacture of golf balls are known in the art. The material selected depends on the play conditions desired for the ball. The core material selected affects how the ball performs and how a golfer perceives the feel of the ball. It is desirable that the ball has a certain degree of compression and durability.
For instance, some golfers desire balls that have a lower compression. A lower compression golf ball has a better perceived “feel” when struck by a golf club. The “feel” component is typically related to a lower frequency sound when the ball is struck.
A lower compression golf ball will have good “feel” when struck with a golf dub but may suffer from a lower coefficient of restitution (COR) or high speed resilience. Also, as the golf ball is struck with a higher club head speed, the golf ball with lower compression will tend to deform to a larger degree, robbing the golf ball of distance. It is thus advantageous to build golf balls that have multiple core layers where one portion of the core is devoted to COR and another portion of the core is devoted to “feel”.
The spin of a golf ball is also very important for generating lift, due to Bernoulli's principle, in flight and control on short shots into the green. Varying the hardness, thickness and COR of the various layers in a multi-layer golf ball core allows the spin attributes to be tuned to the optimum playability while maintaining excellent “feel” and COR.
A designer may select a harder core material and in other instances the designer may select a softer core material, with the golf ball being made of various materials. Balls that have compatible layers will have a relatively longer life expectancy than balls that are made of layers that are incompatble. For example, if a ball is formed with too hard an outer layer and too soft a core layer, the outer layer will crack relatively early in the life of the golf ball and will create dissatisfaction on the part of golfers using the ball. This is known as a modulus mismatch.
The molding of thermoplastic materials with thermoset materials presents a challenge in that the coefficient of thermal expansion (CTE) is typically different between the thermoset material and the thermoplastic material, thus causing differential expansion and molding issues. Mitigating this CTE mismatch is important.
The centering of an inner core within an outer core is no small feat. It requires consistent materials, excellent control over molding conditions and precise molding tools. Also, the workpiece shapes, sometimes called slugs or preforms, are important as to how the materials fill out the mold during compression molding operations. III-formed workpieces in an uncured state will lead to voids and non-centered parts due to poor processing during the compression and curing cycle.
Machines and methods have been developed to manufacture golf balls made of multiple components made of different materials. The different materials within a golf ball may provide different properties that address the considerations noted above. However, the machines and methods to make golf balls made of different materials may experience challenges during manufacture.